From: Eric Biggers <ebiggers@xxxxxxxxxx> Refactor the unkeyed permutation part of chacha20_block() into its own function, then add hchacha20_block() which is the ChaCha equivalent of HSalsa20 and is an intermediate step towards XChaCha20 (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). HChaCha20 skips the final addition of the initial state, and outputs only certain words of the state. It should not be used for streaming directly. Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> --- include/crypto/chacha20.h | 2 ++ lib/chacha20.c | 50 ++++++++++++++++++++++++++++++++++----- 2 files changed, 46 insertions(+), 6 deletions(-) diff --git a/include/crypto/chacha20.h b/include/crypto/chacha20.h index f76302d99e2b..fbec4e6a8789 100644 --- a/include/crypto/chacha20.h +++ b/include/crypto/chacha20.h @@ -19,6 +19,8 @@ struct chacha20_ctx { }; void chacha20_block(u32 *state, u8 *stream); +void hchacha20_block(const u32 *in, u32 *out); + void crypto_chacha20_init(u32 *state, struct chacha20_ctx *ctx, u8 *iv); int crypto_chacha20_setkey(struct crypto_skcipher *tfm, const u8 *key, unsigned int keysize); diff --git a/lib/chacha20.c b/lib/chacha20.c index d907fec6a9ed..6a484e16171d 100644 --- a/lib/chacha20.c +++ b/lib/chacha20.c @@ -1,5 +1,5 @@ /* - * ChaCha20 256-bit cipher algorithm, RFC7539 + * The "hash function" used as the core of the ChaCha20 stream cipher (RFC7539) * * Copyright (C) 2015 Martin Willi * @@ -16,14 +16,10 @@ #include <asm/unaligned.h> #include <crypto/chacha20.h> -void chacha20_block(u32 *state, u8 *stream) +static void chacha20_permute(u32 *x) { - u32 x[16]; int i; - for (i = 0; i < ARRAY_SIZE(x); i++) - x[i] = state[i]; - for (i = 0; i < 20; i += 2) { x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 16); x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 16); @@ -65,6 +61,25 @@ void chacha20_block(u32 *state, u8 *stream) x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 7); x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 7); } +} + +/** + * chacha20_block - generate one keystream block and increment block counter + * @state: input state matrix (16 32-bit words) + * @stream: output keystream block (64 bytes) + * + * This is the ChaCha20 core, a function from 64-byte strings to 64-byte + * strings. The caller has already converted the endianness of the input. This + * function also handles incrementing the block counter in the input matrix. + */ +void chacha20_block(u32 *state, u8 *stream) +{ + u32 x[16]; + int i; + + memcpy(x, state, 64); + + chacha20_permute(x); for (i = 0; i < ARRAY_SIZE(x); i++) put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]); @@ -72,3 +87,26 @@ void chacha20_block(u32 *state, u8 *stream) state[12]++; } EXPORT_SYMBOL(chacha20_block); + +/** + * hchacha20_block - abbreviated ChaCha20 core, for XChaCha20 + * @in: input state matrix (16 32-bit words) + * @out: output (8 32-bit words) + * + * HChaCha20 is the ChaCha equivalent of HSalsa20 and is an intermediate step + * towards XChaCha20 (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). + * HChaCha20 skips the final addition of the initial state, and outputs only + * certain words of the state. It should not be used for streaming directly. + */ +void hchacha20_block(const u32 *in, u32 *out) +{ + u32 x[16]; + + memcpy(x, in, 64); + + chacha20_permute(x); + + memcpy(&out[0], &x[0], 16); + memcpy(&out[4], &x[12], 16); +} +EXPORT_SYMBOL(hchacha20_block); -- 2.19.1.930.g4563a0d9d0-goog
